Light energy delivery head

ABSTRACT

A light energy delivery head is provided which, in one aspect, mounts laser diode bars or other light energy emitters in a heat sink block which is adapted to cool both the emitters and a surface of a medium with which the head is in contact and to which it is applying light energy. In another aspect, various retroreflection configurations are provided which optimize retroreflection of back-scattered light energy from the medium. The size of the aperture through which light energy is applied to the medium is also controlled so as to provide a desired amplification coefficient as a result of retroreflection.

PRIOR APPLICATIONS

This application is a continuation of application Ser. No. 10/052,474,filed Jan. 18, 2002, now U.S. Pat. No. 6,663,620, which is a con ofapplication Ser. No. 09/473,910, filed Dec. 28, 1999, which claimspriority from provisional specification Ser. No. 60/115,447, filed Jan.8, 1999; from provisional specification Ser. No. 60/164,492, filed Nov.9, 1999; and which is also a continuation-in-part of application Ser.No. 09/078,055, filed May 13, 1998, which application claims priorityfrom provisional specification Ser. No. 60/046,542, filed May 15, 1997and Ser. No. 60/077,726, filed Mar. 12, 1998. The contents of all ofthese prior application specifications are incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates to light energy delivery heads, and moreparticularly to a laser diode head or other light energy delivery headfor delivering light energy to a selected depth in a medium,particularly a scattering medium, which head provides improved heatmanagement for both the laser diodes (or other light energy emitter) andthe medium and/or which more efficiently utilizes light energy from thelaser/emitter.

BACKGROUND OF THE INVENTION

Light energy emitters, including lasers, and in particular semiconductordiode lasers, flash lamps, halogen and other filament lamps, etc., arefinding increasing application in medical, industrial, research,governmental and other applications. For many of these applications, thelight energy is to be delivered at a selected depth in a lightscattering medium. Because of the scattering, only a fraction of thelight energy delivered to the surface of the medium reaches the targetarea, with much of the remaining energy being refracted out of themedium and dissipated in the surrounding atmosphere. For a highlyscattering medium such as skin, as much as 50-80 percent of the incidentenergy may be lost due to this back scattering effect, requiring morepowerful light energy emitters/lasers or a larger number ofemitters/diodes lasers (where diode lasers are used), or requiring thatlight energy be delivered over a much smaller area, in order to achievea desired fluence at a target. Utilizing a head with a more powerfulemitter/laser or utilizing a larger number of and/or more powerfulemitters/diode lasers makes the head larger and more expensive andincreases the heat management problems resulting from use of the head.Concentrating the beam to achieve higher fluence with smaller spot sizeor aperture adversely affects the depth in the medium which can bereached by the light energy and can significantly increase the timerequired to perform a given procedure.

U.S. Pat. No. 5,824,023, to Rox Anderson, teaches one way of dealingwith the reflection problem with certain laser or other light energyemitting devices. However, the technique of this patent also results insmall spot sizes and is not readily adaptable for use in certainapplications, such as in laser diode heads. An improved technique istherefore required to permit optimum utilization of the light energyfrom light energy emitting devices in general, and from laser diodes orlaser diode bars of a laser diode head in particular, by recycling orreusing light scattered from the surface of the irradiated medium anddirecting it back toward a desired target area in the medium.

A related problem involves heat management when using a laser diodehead, or other head containing light energy emitters, and in particularthe ability to utilize a common cooling element to cool both the laserdiodes/light energy emitters and the surface of the medium beingirradiated. Surface cooling can be required in various applications,particularly medical applications, since laser energy being delivered ata depth in the medium, for example a patient's skin, must pass throughthe surface of the medium, for example the epidermis of a patient'sskin, in order to reach the target area. Heating of the medium surfacecan cause damage at the surface if suitable cooling is not provided.Prior art systems have either not provided cooling for the mediumsurface or have required separate cooling elements for the diodes andthe medium.

SUMMARY OF THE INVENTION

In accordance with the above, this invention provides, in a firstaspect, a head for applying light energy to a selected depth in ascattering medium having an outer layer in physical and thermal contactwith the head. The head includes a thermally conductive block or mounthaving an energy emitting surface; at least one laser diode or otherenergy emitting element mounted in the block adjacent the energyemitting surface, each of the elements being in thermal contact with themount and being oriented to direct light energy through the energyemitting surface. A thin, transparent, thermally conductive layer isprovided over the light emitting surface and in thermal contacttherewith, the layer being in contact with the outer layer of the mediumwhen the head is applying light energy thereto. Finally, a coolingmechanism is provided for the mount, permitting the mount to sink heatfrom both the elements and the outer layer of the medium. For someembodiments, the thermally conductive layer is a coating formed on thelight emitting surface of the mount.$D_{\min} = \frac{d}{\sqrt{\frac{f \cdot R \cdot r}{f - 1} - 1}}$

For preferred embodiments, the head also includes a reflecting layerformed on the thermally conductive layer, which reflecting layer has anopening formed therein under each element through which light energy maybe applied to the medium. The reflecting layer is preferably between thethermally conductive layer and the energy emitting surface of themount/block, and preferably has an area larger than the area of theblock. In particular, the area of the reflecting layer could be at leastsubstantially as large as the aperture of reflection for scattered lightenergy from the medium. In order to achieve a desired amplificationcoefficient (f) as a result of retroreflection from the reflectinglayer, the aperture through which light energy is applied to the mediumshould have a minimum

dimension where d is a back-scatter aperture increment for a givenwavelength and medium, R is the reflection coefficient of the medium andr is the reflection coefficient of the reflecting layer.

The block for the laser diode head may assume a variety of forms. Inparticular, for some embodiments of the invention, the block has adepression formed therein, with the energy emitting surface being thesurface of the depression, and with each of the elements for someembodiments being mounted to emit light energy substantiallyperpendicular to the depression surface at the point thereon where theelement is mounted. The medium is forced into the depression and intocontact with the surface thereof. The forcing of medium into thedepression may be accomplished by merely pressing the head against asoft deformable medium, such as some areas of a person's skin, orsuction, for example a vacuum line, may be provided to draw the skin orother medium into the depression. The depression may have a variety ofshapes, including being substantially semi-cylindrical or substantiallyrectangular. Where the head is being utilized for hair removal on forexample a person, the depression may be of a size sufficient to permit asingle hair follicle to enter the depression in the plane of therectangular depression.

The reflecting layer may also be formed and utilized for heads which usethe cooled block to cool the diodes or other light energy emitters onlyand not to cool the surface of the medium, for example in applicationswhere a thicker transparent layer is employed or for heads using lightenergy emitting elements other than laser diode bars, for examplefilament lamps or light pipes fed by a suitable light emittingcomponent. For such heads, the reflecting layer would still have areasof the type indicated above and would preferably have an emittingaperture with a minimum dimension D_(min) determined as indicated above.For these embodiments, the transparent layer could be a waveguide ofselected shape, which shape could be a truncated shape which, dependingon desired aperture size, would have, either its larger end or shorterend adjacent the block. Selected sides or walls of the waveguide mayhave an angle dependent reflecting layer to attenuate sharply angledlight energy entering the waveguide.

In still another aspect of the invention, the head may include at leastone energy emitting element mounted to apply light energy to the mediumthrough an aperture, which aperture has a minimum dimension D_(min)defined as indicated above, and a reflecting layer mounted toretroreflect light energy back-scattered from the medium. The aperturemay be circular, with D being a diameter of the aperture, orsubstantially rectangular, with D as the length of a short side of theaperture.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more specific descriptionof preferred embodiments of the invention as illustrated in theaccompanying drawings.

IN THE DRAWINGS

FIG. 1 is partially cutaway, side elevation, semi-schematicrepresentation of a head in accordance with a first embodiment of theinvention;

FIGS. 2A and 2B are enlarged side elevation views of a portion of thehead shown in FIG. 1 for two different species thereof;

FIG. 3A is a cutaway, side elevation, semi-schematic representation of ahead for a first species of a second embodiment, FIG. 3B being anenlarged side elevation view of a portion of the head shown in FIG. 3A;

FIG. 4 is a cutaway, side elevation, semi-schematic representation of asecond species of the second embodiment of the invention;

FIG. 5A is a cutaway, side elevation, semi-schematic representation of athird species of the second embodiment of the invention, FIG. 5B beingan enlarged, side elevation view of a portion of the species shown inFIG. 5A;

FIG. 6 is a cutaway, side elevation, semi-schematic representation of afirst species for a third embodiment of the invention;

FIG. 7 is a cutaway, side elevation, semi-schematic representation of asecond species for the third embodiment of the invention;

FIGS. 8 and 9 are cutaway, side elevation, semi-schematicrepresentations of a third and fourth species of the third embodiment ofthe invention;

FIGS. 10A and 10B are graphic representations illustrating the backscattering effect for a narrow and a wide beam respectively;

FIG. 11 is a graphic representation of the relationship between acoefficient for amplification of irradiance in a scattering medium andbeam diameter for three mediums having different diffuse reflectingcharacteristics; and

FIG. 12 is a cutaway, side elevation, semi-schematic representation of afourth embodiment of the invention.

DETAILED DESCRIPTION

Referring first to FIG. 1, a laser head 10 is shown which contains aplurality of laser diode bars 11, each of which includes a plurality ofemitters 11A and is mounted in a groove 13 formed in a block 12. Block12 may be formed of one or more materials having good thermal conductionproperties, and may be fabricated in a number of ways, all of which arewithin the contemplation of this invention. In particular, block 12 maybe formed of a single material which, in addition to having good thermalconduction properties, is also an electrical insulator, with the sidewalls of grooves 13 being coated or plated with an electricallyconducting material and the diode bars soldered in the grooves, anelectrical circuit being formed between adjacent grooves so that currentmay flow through the diodes without being shorted through block 12.Alternatively, the portion of block 12 between grooves 13 may befabricated of electrically conductive mounts which are secured in asuitable way to a thermally conducting and electrically insulatingsubstrate, the conducting mounts providing an electrical path throughthe diodes and the insulating substrate preventing shorts. Othertechniques for providing an electrical path through the diodes to permitselective energization thereof, while not provided a short circuit paththrough block 12 may also be employed.

Block 12 serves as a heat sink for diode bars 11 and a variety oftechniques may be utilized to remove heat from block 12. These includeproviding one or more channels through block 12 and flowing a fluid,which is generally water but may be some other liquid or gas, throughthe channel to remove heat from block 12. Alternatively, one or morethermoelectric components 14, for example Peltier elements, may beattached to block 12 and utilized to remove heat therefrom.

A transparent element 15 having a high reflectivity mask 16 attachedthereto is mounted to the bottom of block 12, with mask 16 preferablybeing between block 12 and element 15. For a preferred embodiment wherehead 10 is being used for dermatological treatment, the scattering media18 being the skin of a patient, the transparent element is preferablyformed of sapphire or some other material having a good index match withskin, and is preferably either a sapphire coating which is for example 1to 2 microns thick, or a sapphire plate or wafer which is for example 1to 2 mm thick. If component 15 is a plate or wafer, then mask 16 may bea coating of a highly reflective material such as Ag, Cu, Au or amultilayer dielectric coating which is formed using an appropriatecoating technology known in the art, such as lithography, on theplate/wafer 15. Openings 20 (FIG. 2A) are formed in the coating 16 undereach of the diode bar emitter 11A, the openings 20 being only largeenough to permit light from the diode bars to pass unobstructedtherethrough. Keeping slits or openings 20 in reflective layer or mask16 as small as possible is desirable in that it maximizes thereflectivity of the mask and thus, as will be discussed later, optimizesretroreflection of scattered energy from skin or other media 18. Forreasons which will be discussed in greater detail later, reflectivelayer 16 should have a larger footprint than block 12 to further enhancethe reflection back into the media 18 of scattered light or energyemitted therefrom. Since for the illustrative embodiment, mask 16 issupported on transparent plate or wafer 15, this component also has alarger profile. Alternatively, mask 16 may be a thin plate or waferhaving slits 20 formed therein, and transparent component 15 may be alayer of for example sapphire having a thickness in the 1 to 2 micronrange which is coated thereon. In this case, the coating need not extendbeyond the dimensions of block 12; however, it is preferable that thiscoating extend for the full dimensions of mask 16 to provide a goodoptical index match for retroreflected light.

Finally, the apparatus of FIG. 1 includes a box 23 connected to head 10by suitable electrical lines and, where appropriate, plumbing lines (forcooling water) 24. Box 23 may contain appropriate power supplies fordiodes bars 11, control circuitry, fluid pumps where fluid cooling isutilized and other appropriate components. The specific componentscontained in box 23 do not form part of the present invention.

The apparatus of FIG. 1 has several advantageous features over the priorart. First, where the medium 18 is the skin of a patient undergoing adermatological procedure, such as for example the removal of a tattoo, aport wine stain, blood vessel, or other vascular lesion, or hairremoval, it is desirable to cool the epidermis, the surface layer of theskin, to prevent thermal damage thereto during the procedure. In theprior art, a cooling mechanism has been provided for the epidermis inparticular, and for the surface area of a patient's skin in general,which cooling mechanism is separate and independent from the coolingmechanism utilized to sink heat from diode bars 11. These separatecooling mechanisms add to the size, weight, complexity and cost of thesystem in general, and of the delivery head 10 in particular. Theembodiment of FIG. 1 overcomes these problems by having at most a fewmillimeters of material between the block 12, which is cooled bythermoelectric components 14, by a flowing fluid, and/or by othersuitable means, and the patient's skin. Further, the sapphire typicallyused for transparent component 15 has good thermal transfer propertiesso that heat from the patient's skin may easily flow to cooled block 12,and this block may serve as a heat sink for both diode bars 11 and theepidermis of a patient's skin or other surface area of a media 18 towhich light energy is being applied. This arrangement is more compact,simpler and less expensive than prior art heads performing the samefunction.

Further, as illustrated in the Figure, light energy emitted from a diodebar 11 in the form of rays 26 is scattered in media 18, for example in apatient's skin, and at least some of this energy, perhaps 70 percent,depending on the pigmentation of the patient's skin, is reflected backand exits the patient's skin at some angle. Substantially all of thislight impinges on reflecting surface or mask 16, and, since this maskhas a reflectivity approaching 100 percent, substantially all of thislight energy is retroreflected back into the skin. This retroreflectionresults in a roughly 300 percent increase in the light energy or fluencereaching a target at a selected depth in the patient's skin for a givenfluence emitted from diode bars 11. This means that either the sametherapeutic results can be achieved using less diode bars 11 or lowerenergy diode bars 11 or that higher energy, and therefore more effectivetreatment, can be achieved using the same number and power of diodebars. More effective results can thus be achieved for a given size, costand complexity of the diode laser head.

Further, as illustrated in FIG. 10B, light energy entering scatteringmedium 18 over an aperture of size D will, because of beam divergenceand scattering, exit the medium over an aperture D+d, where d is aback-scatter aperture increment and is substantially constant for agiven beam wavelength and medium, regardless of the input aperture D.This is illustrated by FIGS. 10A and 10B, where d is substantially thesame for a thin beam which substantially enters the medium 18 at asingle point and for a wide beam having an aperture D. Thus, as theaperture size D increases, d becomes a smaller percentage of thereflection aperture D+d. For a generally circular aperture, D and D+dare diameters, while for a generally rectangular aperture, these valuesmay be considered to be the length of the smaller side of the rectangle.

The reflection by reflective mask 16 can increase the amount of energyreaching a desired target area by several times. This increase ineffective usage of light energy can be quantitatively described by theincrease in illumination inside scattering medium 18, this increasebeing the ratio (f) between the illumination at an arbitrary targetpoint inside the scattering medium when the reflected light is returnedback to the medium (I_(R)) and when it is not (I_(O)) (i.e.,f=I_(R)/I_(O)). The value of f depends on the reflectance coefficient Rof the scattering medium 18 and the coefficient of reflection of thereflecting mask 16 (r) which returns the scattered light back into themedium (i.e., f=1/1−Rr). However, this known dependence does not takeinto account the influence of beam aperture D; since the beam apertureincreases by d as a result of scattering, amplification coefficient fhas a strong dependence on the aperture D of the incident beam. Inparticular, in accordance with the teachings of this invention, it hasbeen determined that when beam aperture is taken into $\begin{matrix}{f = \frac{1}{1 - {R\quad{r( \frac{D/d}{1 + {D/d}} )}^{2}}}} & (1)\end{matrix}$account, the amplification coefficient f can be approximated by thefollowing equation:Using equation 1 for a given medium, a given reflector, and a desiredillumination amplification, a minimum beam aperture (D_(min)) can bedetermined. D_(min) is generally given by: $\begin{matrix}{D_{\min} = {d \cdot \frac{1}{\sqrt{\frac{f \cdot R \cdot r}{f - 1} - 1}}}} & (2)\end{matrix}$For f=2, this minimum reduces to $\begin{matrix}{D_{\min} = {d \cdot \frac{1}{\sqrt{2 \cdot R \cdot r} - 1}}} & (3)\end{matrix}$With light skin as a reflecting medium, and an incident beam in the redregion of the spectrum, the values in the above equation would be R≈0.7and d≈3 mm. Assuming a reflector with r≈0.95 would then result in aD_(min)=19.5 mm. This suggests that for most applications in laserdermatology, the beam diameter or other appropriate dimension (D) shouldbe greater than 20 mm in order for retroreflection to provide desiredillumination amplification. This is illustrated in FIG. 11 where (f) isshown as a function of the ratio D/d for three reflection environments,with r being 0.95 in each instance, and with R equaling 0.2, 0.5 and0.8, respectively. It is seen that, particularly for the highlyscattering medium having R=0.8, f continues to increase with increasinginput aperture size and may, with retroreflection, provide up to 3.8times the intensity achieved without retroreflection. Assuming d isequal to 3 mm, an input aperture of 20 mm would result in well over twotimes the illumination at the target than if retroreflection were notutilized, and a smaller aperture, for example D=15 mm, would stillprovide significant amplification. Thus, while each individual diode bar11 produces a beam having a dimension in the micron range, head 10 canbe designed to provide a beam having a dimension D which is sufficientto provide a desired illumination amplification. The reflecting surface16 is preferably made large enough so as to fully cover the reflectionaperture which consists of D+d, but may require little or no extensionbeyond the end of block 12 where D is large relative to d.

The embodiment shown in FIG. 1 thus provides at least three significantadvantages over prior art laser diode heads. First, it provides a veryefficient mechanism for cooling both the laser diodes and the surface ofmedium 18 by use of the same cooling mechanism. Second, it provides asimple and effective mechanism for retroreflecting light scattered frommedium 18 over the entire scattering aperture from such medium; andthird it provides a beam aperture which is large enough for efficientillumination amplification as a result of retroreflection while usingradiation sources, for example laser diode bars, which individuallyprovide small beam apertures in the micron range.

FIG. 2B illustrates an alternative embodiment of the invention which maybe useful in some applications. The embodiment of FIG. 2B differs fromthat of FIG. 2A in that transparent layer 15 has been replaced by acylindrical lens 31 mounted under each of the laser diode bars 11.Cylindrical lenses 31 can be supported to the array in ways known in theart including a support bracket or other support structure, eithermounted to or forming part of block 12 at opposite ends of eachcylindrical lens 31. Block 12 also extends somewhat below the bottom ofdiode bars 11 so as to supply structural support for lenses 31 and topermit block 12 to contact the upper surface of medium 18 when slightpressure is applied to block 12 so that the block may still function tocool the surface of the medium. A reflective coating 16 is formed on thebottom wall of block 12 in all areas thereof except the areas directlyunder diode bar emitters 11A, the reflective coating otherwise extendingsubstantially around the entire wall of the recess in which lens 31 ispositioned. Depending on its diameter, a lens 31 may function tocollimate beam 26 emanating from the corresponding diode bar 11 intoparallel rays, as opposed to diverging rays as shown in FIG. 2A, or toconverge such beams toward a focal point which is preferably at thetarget depth. Such a collimating or converging of beam 26 reduces theill effects of scattering on the beam, but does not eliminate suchscattering or significantly reduce the need for reflective surface 16.

FIG. 3 shows an embodiment which differs from that of FIG. 1 in thathigher fluence is required than is provided by the diode bars alone,even with retroreflection. Therefore, energy emitted from transparentlayer 15 is applied to a standard concentrator 34A, which may be ahollow truncated cone or prism, but is preferably a block or slab ofmaterial having a good index match and good heat transfer properties tothe medium 18, for example sapphire when the medium is human skin.Concentrator 34A sacrifices aperture size in order to achieve higherfluence in a manner known in the art. However, the aperture size ismaintained sufficient to conform to the requirements specified inequation (2) above in order to maintain the energy amplification effectsof retroreflection.

The embodiment of FIG. 3 also deals with a second problem in thatscattered light is emitted from the skin at a variety of angles and isreturned to the skin generally at the same angle received. This resultsin a higher concentration of optical energy at the surface of the skinwhere all beams are received and lower energy at depth, where thedesired target is generally located, sharply angled beams only appearingat the surface. Since energy concentrated at the skin surface serves nouseful therapeutic purpose and can cause thermal damage or discomfort ifnot adequately cooled, it is desirable to reduce or eliminate suchsharply angled reflected beams, while not interfering with beamsreflected at angles substantially perpendicular to the medium surfaceand returned to the skin at these angles. This objective is accomplishedfor the embodiment of FIG. 3 by providing a coating 32 on the side wallsof concentrator 34A, which coating has angle-dependent reflectioncharacteristics and may have significantly lower reflectivity thanreflective surface 16. This means that the sharply angled beamsimpinging on surface 32 are attenuated or eliminated, thereby reducingthe beams entering medium 18 at a sharp angle, these beams being onlyharmful and producing no useful therapeutic effect.

While the embodiment of FIG. 3 has the advantages discussed above, italso has two potential disadvantages. First, the aperture for receivingreflected radiation is smaller than the aperture (i.e., D+d) ofreflected radiation, so that this embodiment does not collect allreflected radiation and retroreflect it to medium 18. This results in aslight decrease in the intensity amplification ratio (f) for thisembodiment; however, this disadvantage is mitigated by the fact thatmuch of the energy lost for this embodiment is energy at angles which,even if retroreflected, only contribute to heating the surface of medium18 and do not to have a therapeutic effect or do other useful work at atarget area located at a selected depth in the medium. D being largerthan (d) also minimizes this loss. If desired, reflective extensionscould also be provided for this embodiment to retroreflect all reflectedenergy.

The second disadvantage is that, depending on the thickness ofconcentrator 34A, cooled block 12 may not be effective for cooling thesurface of medium 18. In particular, the time (t) it takes to removeheat from a slab of material having one side in good thermal contactwith the surface to be cooled, an opposite side in good thermal contactwith the cooling medium, in this case the block 12, and a distance orthickness (l) therebetween ist_l²/α  (4)given by:where α is the dielectric slab temperature conductivity coefficient.Where energy is being applied to the slab as successive laser pulsesspaced by a time t_(p), the slab thickness l forl<√{square root over (α·t _(p) )}  (5)cooling to be affected is generally given by:Where the dielectric layer through which optical energy is transmittedand through which it is desired to perform cooling is formed of sapphirehaving a maximum α=15·10⁻⁶ m²/s, and for a typical interval betweenpulses of 0.25 s, this would result in the combined thickness fortransparent layer 15 and concentrator 34A of less than 1.9 mm.Therefore, block 12 being utilized to cool both diode bars 11 and thesurface of medium 18 would normally not be feasible when a concentrator34A is utilized and, if cooling is required, it would normally beachieved by providing a separate cooling mechanism, for example one ormore thermoelectric cooling elements 36, in contact with concentrator34A, and preferably near the lower surface thereof. While only a singlesuch cooling element is shown in FIG. 3, typically four or more suchelements would be provided, spaced substantially evenly around theperiphery of concentrator 34A, to provide uniform cooling thereof.

FIGS. 4 and 5 illustrate two additional embodiments of the inventionwhich differ from that shown in FIG. 3 only in that, in FIG. 4, slab 34Bis an expander rather than a concentrator, while in FIG. 5, slab 34C hasparallel walls so as to not function either as a concentrator or anexpander. Slabs 34A, 34B and 34C therefore permit a single block 12 withdiode bars 11, transparent layer 15 and reflective layer 16 to be usedto achieve a variety of programmable fluence levels. The embodiment ofFIG. 4 is advantageous in that it permits more of the scattered lightemitted from the surface of medium 18 to be collected and recycled thanthe other embodiments, with the embodiment of FIG. 5 having intermediatescattered light collecting capabilities. All three embodiments can haveangle-dependent reflecting side walls 32 so as to reduce orsubstantially eliminate light being emitted at sharp angles. While thereduced reflection of surfaces 32 may be uniform, it is preferable thatthe reflectance from these surfaces be angle-dependent so that lightimpinging on these surfaces at sharper angles are more heavilyattenuated, while light impinging on these surfaces at lesser angles,and therefore light which is more nearly emitted from the surface in aperpendicular direction, are attenuated much less, or in other words aremore fully reflected. Further, reflecting surface 16 for all embodimentscan also be angle-dependent, reflecting more strongly for light comingin at substantially perpendicular angles than for light coming in atsharper angles. While this may be achieved with a single layer coating,it is preferably achieved with a multilayer coating.

FIGS. 6-8 illustrate various species of still another embodiment of theinvention wherein block 12 is replaced with a block 42 having a recess44 formed therein. Grooves 13 are formed in a selected pattern aroundthe perimeter of recess 44. In particular, referring to FIG. 6, theblock 42A has a semi-cylindrical recess 44A formed therein with grooves13 having diode bars 11 mounted therein being arranged in asemi-circular pattern around the periphery of recess 44A, each groove 13and diode bar 11 therein being substantially perpendicular to thecircumference of recess 44A (i.e., substantially parallel to a radii) atthe point on the circumference where they are located. Part of the media18 adjacent recess 44A is brought up therein and into contact withtransparent surface 15 formed on the inside of the recess. Media may bebrought into recess 44A either by pressing block 42A against arelatively soft media 18, for example skin in certain areas, to forcethe skin into the recess, or a source of vacuum may be provided, eitheradjacent the bars near the middle of the recess or between such bars, topull the skin into the recess. Other techniques for forcing skin orother media 18 into the recess 44A may also be employed, either inaddition to or instead of one or more of the two techniques mentionedabove. Finally, the lower portion of block 42A outside of recess 44A hasan angle-dependent reflective coating 32 formed thereon, this surfacereflecting some light back into the skin in an area where it may bescattered to recess 44A.

For the embodiment of FIG. 6, the target area for the light energy wouldbe at roughly the foci of the diode bars, which would generally be apoint near the bottom center of recess 44A. Any light reflected by theskin prior to reaching such a target area would typically be reflectedback into the recess and ultimately returned to the target resulting ina very high illumination increase ratio (f) for this embodiment.

FIG. 7 illustrates an embodiment which differs from that of FIG. 6 inthat the recess 44A in block 42A, instead of merely having a thintransparent layer 15, has a transparent block or lens 40 positionedtherein with a narrow rectangular recess 48 formed in cylindrical lens40. Grooves 13 and the diode bars 11 mounted therein are at a slightlygreater angle so as to have a focus near the upper middle of recess 48.The embodiment of FIG. 7 is particularly adapted for hair removalapplications where a fold of skin having a single hair follicle in theplane of the Figure (there may be several hair follicles in the recess48 along the length of the recess) is in recess 48 at a given time.Vacuum would normally be required to draw such a fold of skin intorecess 48. As for the embodiment of FIG. 6, this embodiment results in ahigh concentration of light, including light reflected from reflectingsurface 16 reaching the target point in recess 48. This effect isfurther enhanced by providing a highly reflective coating 49 on thebottom surface of cylindrical lens 40 which prevents light from exitingthe lens into medium 18. Thus, substantially 100 percent of the lightproduced by diode bars 11 for this embodiment of the invention isapplied to the target area, with virtually no energy being lost toscattering.

FIG. 8 is similar to FIG. 6 except that recess 44B in block 42B has arectangular cross-section rather than a semi-circular cross-section, andgrooves 13 are perpendicular to the walls of recess 44B at the pointswhere they are located. While this embodiment does not result in afocusing of the light at a single point as for the embodiments of FIGS.6 and 7, it does result in a high concentration of light energy inrecess 44B which is applied to medium moved into the recess by pressure,vacuum, or other suitable means.

The embodiment of FIG. 9 is similar to that of FIG. 1 except that ratherthan there being extended portions for layers 15 and 16, there areflexible extensions 52 on each end of the block, which extensions havean angle-dependent reflective coating 32 formed thereon. Vacuum may beused to draw part of medium 18 into the area under block 12 andextensions 52 to provide enhanced radiation of a target area in thisregion or thereunder. The side sections 52 with angle-dependentreflective coating are more effective in directing light energy in the(d) region (FIG. 10B) into the target area than are the flanges of FIG.1.

While not specifically mentioned above, the embodiments of FIGS. 6-9 canalso utilize the cooling technique of FIG. 1 wherein block 12 and/orblock 42 is utilized both to cool diode bars 11 and to cool the surfaceof the skin or other media 18. The embodiment of FIG. 7 is not aseffective for achieving this objective as some of the other embodiments.

While for the embodiments described above, diode bars have been mountedin block 12 of head 10, in some applications other light emitters, forexample filament lamps such as halogen lamps, could be suitably mountedin block 12 in place of the diode bars. Many of the advantages of thisinvention could also be achieved if a light pipe receiving light from alaser or other light emitting source is substituted for each diode bar11 for the various embodiments. For example, FIG. 12 shows a head 10′which differs from that shown in FIG. 1 in that light from a laser orother light energy emitter of suitable power and wavelength is passedthrough a light pipe in lines 24 to a network of light pipes 60 in block12, there being a plurality of light pipes 60 behind each light pipeshown to provide substantially the same light emission pattern as forthe plurality of emitters 11A of each diode bar 11. The minimum aperturesize D to achieve a selected amplification (f) from retroreflection isalso applicable to substantially any laser or other light energyemitting head used on a scattering medium, including those shown invarious prior patents and applications including U.S. Pat Nos.5,595,568; 5,735,844; 5,824,023, and application Ser. No. 09/078,055,FIG. 4 of which, for example, shows a head which may be used inpracticing the teachings of this invention, but which differs from FIG.12 in that the light pipes are angled to focus the light energy. Wherelight pipes are utilized, transparent layer or element may not berequired, and reflective coating 16 can be applied directly to thebottom surface of block 12, with openings in the coating being providedunder each light pipe.

Further, transparent layer 15 is preferably spaced by at least severalmicron, for example 50-100 microns, from the diode bars to assureagainst shorting of the laser bars, and this space may be filled withair or other gas, or with a liquid or solid insulating material which istransparent at least in the areas under the openings or slits in thereflective layer 16. For this embodiment, the spacing may be such thatcooling of the medium from block 12 is no longer possible.

An invention has thus been disclosed, including a number of embodimentsand various species of each embodiment, which provides a simpler coolingmechanism for certain embodiments for the surface of a medium undergoinga laser or other optical energy procedure and which also provides moreoptimum, and in some cases substantially optimum, use of light energyproduced by diode laser bars, or other optical energy source, even whenthe light is being delivered to a highly scattering medium, by designingthe device to provide an adequate input aperture and suitable mechanismsfor retroreflecting such light. Further, while a number of embodimentsand species thereof have been disclosed, it is apparent that these arebeing provided for purposes of illustration only and that other similaror equivalent mechanisms might also be employed. Thus, while theinvention has been particularly shown and described above with referenceto preferred embodiments and species, the foregoing and other changes inform and detail may be made therein by one skilled in the art withoutdeparting from the spirit and scope of the invention, which is to bedefined only by the appended claims.

1. A head for applying light energy to a selected depth in a scatteringmedium having an outer layer in physical and thermal contact with saidhead including: a thermally conductive mount having an energy emittingsurface; at least one optical energy emitting element mounted in saidmount adjacent said energy emitting surface, each said element being inthermal contact with said mount and oriented to direct light energythrough said surface; a thin, transparent, thermally conductive layerover said surface and in thermal contact therewith, said layer being incontact with said outer layer of the medium when the head is applyinglight energy thereto; and a cooling mechanism for said mount, permittingsaid mount to sink heat from both said at least one element and saidouter layer of the medium.
 2. A head as claimed in claim 1, including areflecting layer on said thermally conductive layer, said reflectinglayer having an opening formed therein under each said at least oneelement through which light energy may be applied to said medium.
 3. Ahead as claimed in claim 2, wherein said reflecting layer has a largerarea than the area of said mount.
 4. A head as claimed in claim 3,wherein the area of said reflecting layer is at least substantially aslarge as an aperture of reflection for scattered light energy from saidmedium.
 5. A head as claimed in claim 2, wherein light energy is appliedto said medium through an aperture, wherein there is a desiredamplification coefficient f as a result of retroreflection from saidreflecting layer, wherein the medium and the reflecting layer havereflecting coefficients R and r respectively, and wherein the minimumvalue D_(min) for a dimension D of the aperture is$D_{\min} = {d \cdot {\frac{1}{\frac{\sqrt{f \cdot R \cdot r}}{f - 1} - 1}.}}$6. A head as claimed in claim 1, wherein said mount has a depressionformed therein, said energy emitting surface being the surface of saiddepression, each of said element being mounted to emit light energysubstantially perpendicular to the depression surface at the pointthereon where the element is mounted, said medium being forcible intosaid depression and into contact with the surface thereof.
 7. A head asclaimed in claim 6, wherein said depression is substantiallyhemispherical in shape.
 8. A head as claimed in claim 6, wherein saiddepression is substantially rectangular in shape.
 9. A head as claimedin claim 1, wherein said thermally conductive layer is a coating formedon said light emitting surface.
 10. A head as claimed in claim 1 whereineach said element is a diode laser bar.